1. Field of the Invention
The invention concerns a lighting or signaling device for a motor vehicle which comprises a plate for guiding the light.
The invention more particularly concerns a lighting or signaling device for a motor vehicle which is capable of emitting a linear beam essentially in the direction of an optical axis, and which comprises:
a point light source that emits light rays radially around a source axis; and
a light ray guiding plate that comprises an edge for inputting the light rays, a front edge for outputting the light rays tangentially to the light guiding plate, and a rear edge for reflecting the light rays coming from the light source in the direction of the output edge.
2. Description of the Related Art
It is common practice to group several lighting and/or signaling functions together in a single enclosure, so as to simplify the electrical wiring for these different functions in a motor vehicle.
Moreover, the shape of the lighting and/or signaling lights plays a leading role in the search for a style and original aesthetics which will enable the motor vehicle to be recognized from a distance.
To solve these problems, equipping the vehicle with light guides is known. A light guide is a cylinder of transparent material which forms a kind of “pipe” into which the light rays enter via a first input end. The light rays are then guided along the light guide by successive total reflections on its cylindrical outer face.
A rear portion of the cylindrical face of the light guide comprises irregularities, such as diffusion flutes, which make it possible to diffuse some of the light rays towards the front so that some of the diffused light rays exit the light guide by passing through the opposite portion of the cylindrical face in order to form a light beam.
The light guide can for example be shaped as a ring that surrounds the front boundary of a low beam headlamp so as to emit an annular light beam. The input end portion of the light guide is then bent so that the light ray input end is arranged outside the ring formed by the light guide.
However, such a solution does not make it possible to obtain a high intensity light beam. This is because the light rays emitted by the light source are guided in a random and unordered manner inside the light guide. Moreover, only some of the light rays are diffused to the outside by the irregularities. Consequently, the light beam obtained by such a device is very weak even if the light source arranged at the input end of the light guide is very powerful.
However, certain lighting and signaling functions require a very intense light beam in order to comply with current regulations. The light guide is therefore not suitable for implementing such functions.
Moreover, the appearance of the annular beam obtained is highly non-uniform in particular for the following two reasons.
On the one hand the material constituting the lighting or signaling device brings about some absorption of the light rays that pass through it, which results in losses that become greater with the distance away from the light source. As a result the brightness in the vicinity of the light source is greater than at a distance from this source, hence a uniformity fault.
On the other hand some of the light rays introduced into the light guide via the bent input portion directly reach the opposite face of the light guide thus causing the appearance of a spot that is very bright compared with the rest of the annular beam.
There is, therefore, a need to provide an improved lighting or signaling device.